Synthesis and structure determination of products from addition of dimethyl acetylenedicarboxylate to 2,3-dihydro-2-thioxoquinazolin-4(1H)-one. X-Ray molecular structure of the dimethyl esters of 1,2-dihydro-5-oxo-5H-thiazolo[3,2-a]quinazoline-1,2-dicarboxylic, 2,3-dihydro-5-oxo-5H-thiazolo[2,3-b]quinazoline-2,3-dicarboxylic, and 5-oxo-5H-thiazolo[2,3-b]quinazoline-2,3-dicarboxylic acids

Abstract

The addition of dimethyl acetylenedicarboxylate to 2,3-dihydro-2-thioxoquinazolin-4(1H)-one afforded four main cycloadducts, the structures of which were unequivocally solved by ¹³C n.m.r. spectroscopy and confirmed by X-ray crystallographic analysis. The products were identified as dimethyl 1,2-dihydro-5-oxo-5H-thiazolo[3,2-a]quinazoline-1,2-dicarboxylate, dimethyl 2,3-dihydro-5-oxo-5H-thiazolo[2,3-b]quinazoline-2,3-dicarboxylate, dimethyl 5-oxo-5H-thiazolo[2,3-b]quinazoline-2,3-dicarboxylate, and tetramethyl 2,2′-(1″,2″,3″,4″-tetrahydro-4-oxo-2-thioxoquinazoline-1″,3″-diyl)difumarate.